"I've thought about it for a long time, but the timing became more clear to me over the course of the last few months," he said.

"We worked hard on our strategy process, our org process. And frankly I had no time to think about it during all of that... I would say my thinking has intensified really over the last couple, two, two and a half months, something like that."

The CEO added that Bill Gates "respected" his decision and that he has no immediate plans for the future.

"My whole life has been about my family and about Microsoft," he said.

"And I do relish the idea that I'll have another chapter, a chapter two, if you will, of my life where I'll get to sort of experience other sides of life, learn more about myself, all of that, but it's not like I leave with a specific plan in mind."